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Gun-Operated Alarm Clock 



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Gun-Operated Alarm Clock 



Written By: Roger Ibars 



f TOOLS: 

Artist paintbrush (1) 

Multimeter (1) 

Rotary tool and bits (1) 

Round metal file (1) 

Screwdrivers (1) 

Side cutter (1) 

Soldering equipment (1) 

Strong glue (1) 

or a glue gun and hot glue 

Toothbrush (1) 

Wire stripper (1) 

cotten cloth (1) 



© PARTS: 

• Electric tape (1) 

• Poster putty (1) 

• Spray plastic polish (1) 

the kind used to shine your car 
dashboard 

• Kitchen soap (1) 

• Digital clock radio (1) 
must be fully functioning 

• Multi-way cable with at least four 
conductors (1) 

/ used a fancy SCART cable consisting 
of 9 color-coded,stranded wires wrapped 
in a grounded, metallic Mylar screen, all 
sheathed in black PVC to an overall 
diameter of 6mm. This top-quality choice 
can be found in hi-fi stores and will give 
you a nice curvature of the cable. 

• Small tilt switches (5) 

/ recommend non- mercury switches for 
environmental reasons. These cost 
about $1 each, and are available from 



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Gun-Operated Alarm Clock 



electronics suppliers such as Farnell 
(farnell.com), Newark InOne 
(newark. com) , Rapid (rapi don line, com) , 
and RS (rswww.com). For models with 
just one lead, the case works as the 
other contact. 

Light gun (1) 

/ particularly like the Nintendo Zapper, 
the SEGA Light Phaser, the Atari G1, the 
Konami Justifier, and the Sinclair 
Magnum (my choice). Make sure there's 
enough space inside the grip to fit the 
circuit that we are going to build. 

Small perfboard (1) 

available from electronics suppliers, 

including RadioShack 



SUMMARY 

Clock radios are everyday hated devices that designers seem to ignore, judging by how little 
their features and user interfaces have changed. This project adds a new capability, letting 
would-be sleepyheads enjoy a human-machine interaction of a different sort. Don't worry, 
we're not going to connect your clock to an MP3 player and play mellow New Age sounds. 
We're going to shoot the alarm off. With a gun. Wake-up time is now payback time. 

We'll base the project around a digital clock radio and a light gun for gaming; huge selections 
of both of these are available inexpensively second-hand, with many beautiful and well 
designed examples. To enable our FPSI (First Person Shooter Interface), we'll outfit the gun 
with five tilt sensors, arranged at different angles on a small circuit board. A cable tethers 
the gun to the clock and carries your tilt and trigger signals to the clock's time and alarm 
control button contacts. 



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Gun-Operated Alarm Clock 






• Our control circuit uses tilt switches to detect the gun's position. 

• Tilt switches contain a metal ball or a conductive liquid (such as mercury) that rolls 
inside a small capsule. When the switch's contacts point downward, the conductor 
bridges the contacts, closing the switch. Turn the switch upside down, and the conductor 
falls away from the contacts, opening the connection. 

• The tilt switches are arranged in a plane perpendicular to the gun's barrel, to detect 
the approximate rotation of the handle when the gun is aimed forward (its "roll" in 
aeronautical terms). The gun doesn't need to point at the clock to work (but it's more 
satisfying that way). 

• The tilt circuit is wired into the clock radio to spoof three buttons: Alarm, Hour, and 
Minute. (We ignore the Snooze button.) Tilting the gun at different angles lines up 
connections through the tilt switches that bridge different buttons' contacts. Pulling the 
trigger closes a shared ground connection, completing the connection as if you pressed 
the button (or button combination). 

• CAUTION: Do not work on the alarm clock while it is plugged in, or you risk serious 
and possibly fatal electric shock. 





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Gun-Operated Alarm Clock 







Unplug the clock radio. 

Disassemble the case. Carefully unscrew the four screws concealed by wells on the back, 
and separate the electronics from the plastic parts. To avoid damaging the plastic, choose 
a screwdriver that fits well, press down firmly, and turn slowly. 

Marvel at the design details and quality! The shell is extremely well-crafted, with neat 
cavities for the screws and an elegant, raised icon for the power cord. The controls even 
resemble a face. This clock is full of design generosity, which is quite rare nowadays. 



Untie the electric cable, and separate the electronic parts from the plastic shell. 

Remember exactly how you took apart the electronics block and untied the electric 
cable, so you can put it all back together later. 



it 



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Gun-Operated Alarm Clock 




• Use the paintbrush to clean the dust accumulated on the electronics. 

• Clean the plastic case with the toothbrush and kitchen soap. The bristles won't damage or 
scratch the surface. Take your time to enjoy cleaning every corner! Let all pieces dry 
thoroughly. 

• NOTE: After the pieces dry, spray them with plastic polish, following the 
instructions on the can. 

• Wait a few minutes after spraying, then polish the surfaces with a clean cotton cloth. You'll 
be amazed how new they'll look! Now your alarm clock is ready for more serious work. 




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Gun-Operated Alarm Clock 





On the front half of the plastic shell, measure and mark a point to drill near the base and 
centered below the display. Protect the surface around the hole area with electrical tape, in 
case your drill skips away from its proper destination. 

Find a drill bit that's a bit thinner than your multi-conductor cable and drill the hole. 

NOTE: This is the riskiest part of the work: drilling holes for the cable through the 
clock's case. (I see some vintage collectors out there raising their hands in 
objection.) 

Widen the hole with the round file. Keep widening slowly until the cable can just go through 
the hole with a bit of pressure. We don't want a hole bigger than the cable. 

Drill and widen a second hole in the plastic shell about 1" to the left and slightly back from 
the first hole, in the interior wall that holds the battery case (see picture below right). The 
cable will enter the first hole and make a sharp left turn into this hidden hole as it routes its 
wires around to the back of the clock. 



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Gun-Operated Alarm Clock 







Strip about 16" of sheathing off of each end of the cable, to reveal the color-coded wires 
inside. Pass one end of the cable through the holes you just drilled. 

Use hot glue or another strong adhesive to fix the cable firmly in place, keeping the 
individual wires free inside the main compartment. Leave it neat and strong since this 
cable is going to be used. 

Put the electronics block back into the front half of the case. Now we are ready to hard- 
wire the color cables to the clock switches. 



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Gun-Operated Alarm Clock 




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Gun-Operated Alarm Clock 




If you aren't modeling a 
Panasonic RC-70, don't 



> 

/* 



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worry, because almost 99% of 
digital clocks work the same way. 
Just remember that each button 
has 2 connections, which come 
into contact with each other when 
you press the button. You want to 
extend these connections so that, 
instead of closing the circuit with 
the button, you'll be using the light 
gun. 

• Find the buttons that control the 
essential functions: set time and 
alarm (hours and minutes), and 
alarm off. The RC-70 uses just 3 
buttons for these: Alarm, Hour, and 
Minute. The Alarm button does 
double duty, shutting off the alarm 
and switching the Hour and Minute 
buttons from "time-set mode" (the 
default) to "alarm-set." Some clock 
radios use a switch instead of a 
button to change between time-set 
and alarm-set modes. 

• Locate the essential buttons' 
contacts, 2 per button, and use a 
multimeter to follow each of them 
out to a solderable connection 
point. With the RC-70, all 3 buttons 
shared a common ground, so I 
needed to find a total of 4 
connection points. 

• Solder wires from your cable to the 
contact points, using the color 
coding to track what goes where. 

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Gun-Operated Alarm Clock 



Following convention, I connected 
the cable's black wire to the shared 
ground, and designated colors for 
the 3 button-specific connections. 

Organize and fix all the color 
cables between the free spaces of 
the clock. Trim extraneous cables 
to get them out of the way. Avoid 
placing cables near parts that get 
warm, such as the power 
converter. 

Reassemble the clock and screw it 
back together. 

Test the clock by plugging it in and 
touching together the other ends of 
the cable wires you just soldered. 
Confirm that bridging the wires 
mimics the functions of the buttons 
you connected them to. If you 
didn't make any big mistakes, 
everything should work! Don't 
worry about touching the wires with 
your fingers, because the current 
going through them is very low. 
Once it's working, unplug it again. 



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Gun-Operated Alarm Clock 




Take the light gun apart, and clean and shine it up the way you did with the clock radio. 

Cut a rectangle of perfboard that's big enough to carry the 5 tilt switches flat, but narrow 
enough to fit facing backward inside the handle. For my Sinclair Magnum, my board was 
about 3"x22". 

If your clock radio is an RC-70 or work-alike, arrange the tilt switches on the perfboard as 
shown. Leave some extra room around each switch to let you bend and fine-tune their 
positions later. 

Following the wiring diagram solder the tilt switches into place and connect them to the 
cable wires. Don't worry about which sides you connect; the switches are functionally 
symmetrical. 

Connect the ground to each sensor section and route it through the trigger switch contacts 
in the gun. To make my circuit more readable, I routed all wiring from the cable and trigger 
through the front of the board, at the edges. I also split 1 ground coming from the trigger 
and connected it in 2 places. 



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Gun-Operated Alarm Clock 







Use poster putty to hold the tilt circuit in position inside the gun-half with the trigger. Plug 
in the clock radio, and test the interface by tilting and firing. Experiment with different firing 
angles, and bend the tilt switches around to refine their operation. 

When the tilt switches work together properly, glue them in place, and then glue the circuit 
board into the gun handle. Re-assemble the gun. 

Set the time, set the alarm to +1 minute, wait a minute, and FIRE! 



This project first appeared in MAKE Volume 08 , page 100. 



This document was last generated on 201 2-1 1 -02 05:36:36 PM. 



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